The role of glycine homeostasis in epilepsy has largely been neglected, not only in our appreciation of pathophysiological mechanisms, but likewise in therapeutic drug development efforts. This proposal is based on promising preliminary data from our laboratory, which demonstrate an unprecedented anticonvulsant role of glycine augmenting drugs. Specifically, we will evaluate whether glycine augmenting drugs, which are already in clinical development for schizophrenia, could be used for the treatment of seizures in temporal lobe epilepsy (TLE). This grant will fill a critical gap in knowledge and proposes that disruption of glycine homeostasis is implicated in the pathophysiology of TLE and that therapeutic glycine augmentation is a novel pharmacological principle for the treatment of TLE. In hippocampus, glycine is largely regulated by its specific transporter GlyT1, and fulfills a dual role as homeostatic regulator of neuronal excitability by binding to glycine receptors (potentially anticonvulsive) and the glycineB-site of N-methyl-D-aspartate receptors (potentially procognitive). This goal-oriented proposal will test the CENTRAL HYPOTHESIS that therapeutic glycine augmentation represents a novel strategy for seizure control in temporal lobe epilepsy (TLE). Our preliminary data demonstrate that glycine homeostasis is perturbed in a mouse model of TLE. Further, we demonstrated that engineered mice with conditional disruption of GlyT1 (to increase hippocampal glycine) have increased seizure thresholds, whereas a GlyT1 antagonist robustly suppressed chronic seizures in a mouse model of TLE. In addition, our data document a profound pro-cognitive effect of genetic GlyT1 disruption. Key experimental tools required to test our hypothesis include genetic tools to disrupt GlyT1 function, GlyT1-inhibiting drugs, rodent models of acute seizures and of TLE, and relevant behavioral tests. Our research goals will be addressed in three Specific Aims: (1) Identify the mechanisms of seizure suppression by glycine. (2) Test the prediction that acute glycine augmentation prevents seizures in rodents. (3) Test the hypothesis that chronic GlyT1 inhibition improves seizures and cognitive function in TLE. Expected outcome and impact: A combination of mechanistic and therapeutic studies will allow us to determine whether GlyT1 antagonists might be useful alternative drugs for the treatment of TLE. We will make novel and innovative use of GlyT1 inhibitors that have already been tested in clinical trials (phase II/III) to treat cognitive symptms in schizophrenia. Identification and characterization of a novel anticonvulsant role of existing drugs will open new opportunities for clinical translation of therapeutic glycine augmentation as novel pharmacological principle for epilepsy therapy. The expected benefit of therapeutic glycine augmentation is seizure control combined with a pro-cognitive activity, which sets therapeutic glycine augmentation apart from conventional antiepileptic drugs, which tend to be associated with cognitive impairment as prominent side effect.